1. Field of the Invention
The present invention relates to optical communications and, more specifically, to all-optical data recognition and routing.
2. Description of the Related Art
One of the bottlenecks in the growth of the internet is the gap between the rate of increase of internet traffic and the slower rate of increase in edge router capacity. The use of optics in data routing has been investigated to relieve the burdens put on routers associated with repeated optical-to-electronic and electronic-to-optical conversions and the intervening electronic data processing. For example, performing header recognition of even a part of standard 32-bit IP headers all optically can greatly simplify the structure of routers and reduce their power consumption.
Optical correlation techniques using passive optical filters are among the most promising ways of implementing all-optical header recognition. Passive optical filters can be realized using a variety of technologies, such as planar-lightwave-circuits (PLCs) or fiber Bragg gratings. When the spectral response of the filter matches the complex conjugate of the spectrum of the target data pattern, an autocorrelation syndrome pulse is generated, which can be subsequently used for control of data routing or other data processing.
One of the key challenges in passive optical correlation techniques has been the difficulties in scaling the filters to process a large number of header bits. Passive correlator filters are typically constructed using multiple optical delays with the longest temporal delay proportional to the number of header bits. However, the requirement for wavelength stability has not been quantitatively analyzed previously, while it is expected to vary quite nonlinearly with respect to the number of bits. Another challenge is the inability of passive correlation techniques to distinguish arbitrary on-off-keyed (OOK) data bits. In the past, a special set of orthogonal code words that generate mutually distinct correlation signals was used for OOK signals, which limits the number of header patterns that can be used for OOK.